1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine provided with a variable valve timing mechanism and a variable valve timing control device which serve to continuously adjust the opening and closing timing of an intake valve in accordance with an operating state of the internal combustion engine.
2. Description of the Related Art
In general, as a control apparatus for an internal combustion engine including a variable valve timing control device for adjusting the opening and closing timing of an intake valve of an internal combustion engine, there has been proposed one that corrects basic timing based on a mechanically engaged position of a variable valve timing mechanism (see, for instance, a first patent document: Japanese patent No. 3395240).
In addition, as a device for correcting basic timing by directly detecting the opening and closing timing of an intake valve, there has been known one which includes a variable valve timing mechanism that adjusts the opening and closing of an intake valve based on basic timing, an operating state detection part that detects the operating state of an internal combustion engine, a driving control part for driving and controlling the variable valve timing mechanism, an intake negative pressure detection part that detects an intake negative pressure (depression at an engine manifold) of the internal combustion engine, a negative pressure difference storage part that stores a basic negative pressure difference before and after timing adjustment, a correction time driving control part for driving and controlling at the time of correction, and a basic timing correction part (see, for instance, a second patent document: Japanese patent No. 3161152).
In the variable valve timing control device described in the above-mentioned second patent document, the intake valve is driven, in synchronization with the rotation of the internal combustion engine at timing with a predetermined phase difference, to open and close an intake pipe leading to a combustion chamber of the internal combustion engine.
The variable valve timing mechanism is constructed in such a manner as to be able to adjust the opening and closing timing of the intake valve, so that the opening and closing timing of the intake valve is continuously adjusted to an advance angle side and a retard angle side with reference to a predetermined basic timing.
The driving control part drives and controls the variable valve timing mechanism on the basis of the detection result of the operating state detection part.
The intake negative pressure detection part detects the intake negative pressure (i.e., negative pressure in the intake pipe) that varies in accordance with the adjustment of the opening and closing timing of the intake valve.
The negative pressure difference storage part stores a basic negative pressure difference between a first intake negative pressure at the time when the variable valve timing mechanism becomes a predetermined basic state in which the intake valve is opened and closed at the basic timing, and a second intake negative pressure at the time when the variable valve timing mechanism is controlled to be driven to open the intake valve so as to advance the opening and closing timing thereof a predetermined amount from the basic timing.
The correction time driving control part once nullifies the driving control of the variable valve timing mechanism by the driving control part when the operating state of the internal combustion engine (based on the detection result of the operating state detection part) is in a prescribed and predetermined state, and sets the variable valve timing mechanism to a predetermined state in which the intake negative pressure in the intake pipe becomes the first intake negative pressure, after which the variable valve timing mechanism is controlled to be driven to advance the opening and closing timing of the intake valve.
When an actually measured negative pressure difference between an intake negative pressure measured based on the detection result of the intake negative pressure detection part when the operating state of the internal combustion engine is in the predetermined state and an intake negative pressure measured at the start of the driving control of the correction time driving control part exceeds the basic negative pressure difference stored beforehand in the negative pressure difference storage part, the basic timing correction part corrects the basic timing based on the state of the variable valve timing mechanism at that time.
The conventional apparatus described in the above-mentioned second patent document is advantageous in that it corrects the basic timing by directly detecting the opening and closing timing of the intake valve, so it can perform correction with a higher degree of precision than the conventional apparatus described in the first patent document can do in which the basic timing is corrected at the mechanically engaged position of the variable valve timing mechanism.
Although in the variable valve timing control device described in the above-mentioned second patent document, the valve timing mechanism is controlled to be driven so as to detect the second intake negative pressure after the intake negative pressure in the intake pipe is set to a predetermined state, i.e., the first intake negative pressure, the intake negative pressure changes when the operating state (for instance, rotational speed) of the internal combustion engine changes even if the valve timing is constant.
Accordingly, if the engine operating state changes from the time when the intake negative pressure in the intake pipe is set to the predetermined state (the first intake negative pressure) until the detection of the second intake negative pressure, the relation between the valve timing and the intake negative pressure can not be correctly acquired.
Thus, in the device described in the above-mentioned second patent document, in order to correctly acquire the relation between the opening and closing timing of the intake valve and the intake negative pressure, an idling operation, for example, is set as an operating condition in which the engine operating state can be assumed to be unchangeable over a fixed period of time, and the valve timing is corrected in the idling state of the engine.
As described in the second patent document, the variable valve timing control device in the conventional internal combustion engine control apparatus corrects the valve timing in an operating condition (idling state), in which the engine operating state does not change over a fixed period of time, so as to correctly obtain the relation between the valve timing and the intake negative pressure, so there is a problem that it is impossible to perform correction at times other than during idling operation.
In addition, during idling, the flow rate or speed of air sucked into the internal combustion engine becomes slow, so there is another problem that when the valve timing is changed to an advance angle side in the idling state of the engine, the scavenge performance of the exhaust gas of the internal combustion engine is reduced to generate defective combustion, thus resulting in an increase of harmful components in the exhaust gas.
Further, in the conventional apparatus described in the above-mentioned second patent document, the degree of opening of an idle speed control valve is fixed at the time of execution of a correction operation, so when a rough idle state is generated due to the defective combustion resulting from the operation of the variable valve timing mechanism, the rotational speed of the internal combustion engine can not be maintained at a predetermined target idle rotational speed.
Accordingly, there arise the following problems. That is, the intake negative pressure varies according to abnormal rotational fluctuations, so there is a consequent possibility of causing engine stall, as a result of which it becomes impossible to correctly acquire the relation between the opening and closing timing of the intake valve and the intake negative pressure, so the basic timing of the variable valve timing mechanism is not able to be corrected with a high degree of precision.